Solar Eclipse Will Test European Power Grids

A partial eclipse of the sun headed for Europe next Friday has grid operators in a tizzy.  On the morning of March 20 Europe's skies will darken for the first time since solar power became a meaningful piece of some countries’ power supply, and the impact could be dramatic.

“It’s a very, very big challenge for the transmission system operators in Europe,” says Enrico Maria Carlini, Head of Electric System Engineering for National Dispatching at Rome-based Italian transmission system operator Terna.

The Brussels-based European Network for Transmission System Operators for Electricity (ENTSO-E) judges in an eclipse impact analysis released last month that it poses a, “serious challenge to the regulating capability of the interconnected power system.”

While an eclipse markedly reduced solar generation in western North America last October according to energy tracking firm Opower, Europe’s far greater levels of solar power make for bigger stakes.  ENTSO-E projects that the moon’s jaunt across the sun’s path next Friday could slash more than 30 gigawatts (GW) of solar generation in Continental Europe over one hour if clouds are scarce and solar generation is high.  That’s the equivalent of turning off 30 big coal or nuclear power stations.

The moon’s shadow will be deepest in Northern Europe, but power grid impacts could spread across Continental Europe via the region’s 27-nation interconnected AC grid.  Because the grid operates synchronously, failure by any transmission system operators (TSOs) to keep supply and demand in balance as solar power plummets and then races back will throw off the grid’s 50-hertz AC frequency Continent-wide.

In a worst-case scenario such frequency disruption could snowball.  Many of Europe’s early distributed generators such as solar systems and wind turbines were programmed to shut off if grid frequency diverged from 50 hertz by just one percent, and could be triggered by the solar losses.  Retrofitting with smart inverters that can withstand much bigger AC signal glitches is a work in progress.  ENTSO-E warned in January that frequency-induced blackouts remain a “significant operational risk”.

ENTSO-E’s analysis also flags a threat of transmission lines overloading during the eclipse as flow patterns over the meshed grid shift rapidly.  Overload risk will be most heightened in the region around solar heavyweights Germany and Italy, which together host over three-fifths of the European grid’s solar capacity.

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